The specific activity of the fatty acid cyclooxygenase catalyzing the initial step in prostaglandin formation is 2-5 fold greater in guinea pig and sheep uteri at the onset of luteolysis than during earlier stages of the estrous cycle. We have recently established that this increased activity represents an increase in the level of cyclooxygenase protein and not a decrease in the level of some enzyme inhibitor. We distinguished between these possibilities using rabbit anti-cyclooxygenase serum to determine if uterine cyclooxygenases from animals in different stages of the estrous cycle were equivalent immunochemically. We are implementing a tissue explant system which can then be used to determine the rates of cyclooxygenase synthesis and degradation using common radioimmunochemical procedures. We are continuing studies designed to identify which uterine cell type contains the increased amounts of cyclooxygenase observed during later stages of the ovine estrous cycle using an immunohistofluorescence procedure. A portion of the proposed research will involve our continued use of immunohistochemical techniques to localize sites of prostaglandin formation within mammalian tissues other than the uterus particularly those involved with female reproductive function.